Patent Document 1 discloses a semiconductor optical device. In the semiconductor optical device, a piezoelectric field in a strained layer does not occur at all in a direction tilted at an angle of about 40 degrees, 90 degrees, and 140 degrees defined with reference to the [0001] direction. Accordingly, a plane orientation is selected within the angle range of 30 to 50 degrees, 80 to 100 degrees, or 130 to 150 degrees. Epitaxial growth occurs onto the surface of a substrate on which little or no piezoelectric field is generated in a strained quantum-well structure.
Patent Document 2 discloses a semiconductor light-emitting device. This semiconductor light-emitting device is formed on a nonpolar plane. The nonpolar plane encompasses a {11-20} plane, a plane tilted from the {11-20} plane at an angle in the range of −5 to +5 degrees, a {1-100} plane, or a plane tilted from the {1-100} plane at an angle in the range of −5 to +5 degrees.
Non-Patent Document 1 discloses a theoretical study of dependence of the piezoelectric effect on crystal orientation in an InGaN/GaN heterostructure of a wurtzite structure. A strained layer grown in a crystal orientation at an off-angle of 39 degrees or 90 degrees with reference to (0001) does not induce the longitudinal component of the piezoelectric field. Furthermore, Non-Patent Document 2 discloses the effect of crystal orientation in relation to electrical characteristics of an InGaN/GaN quantum-well of a wurtzite structure. The internal electric field of the InGaN/GaN quantum-well structure changes its sign around at an off-angle of about 55 degrees.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 11-112029 (Japanese Patent Application No. 09-263511)
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 10-135576
[Non-Patent Document 1] Jpn. J. Appl. Phys., vol. 39 (2000), pp. 413-416. Part 1. No. 2A, Feb.
[Non-Patent Document 2] J. Appl. Phys., Vol. 91, No. 12, 15 Jun. 2002, 9904-9908.